Manufacturing oxide cathodes



Patented Oct. 18, 1932 meant V ERICH WIEGAND, F BERLIN-WAIDMANNSLUST, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF YORK MANUFACTURING OXIDE CATHODES No Drawing. Application filed June 30, 1931, Serial No. 548,036, and in Germany July '16, 1930.

One known method of manufacturing oxide cathodes consists inprecipitating alkaline earth metal from the vapor phase onto an unheated carrier filament and oxidizing the said metal by subsequently heating the carrier filament in oxygen, for the purpose of obtaining alkaline earth oxide. While this process may produce cathodes of relatively long life and high electron emissivity, it has been found that notwithstanding the extreme care exercised in their manufacture, such cathodes are not accurately reproducible on a quantity production basis, in so far as their electron emission is concerned. All attempts made to the present day to obviate this disadvantage have not been entirely successful and no satisfactory explanation has been offered for this failure. However, in accordance with my invention, cathodes of considerably greater uniformity are obtained when the filament is activated by following another procedure. The new process consists in coating the oathode carrier with an oxygen compound and heating the carrier to such a temperature when the alkaline-earth metal is in the form of vapor that no appreciable quantity of alkaline-earth metal (in solid or liquid form) V is de osited on the said carrier but the concathode must be heated when the metal is in the vapor state depends upon the nature of the alkaline-earth metal used. A temperature of the order of 900 C. is generally 'sufilcient when using barium metal, but must be somewhat higher in the case of calcium and strontium owing to their relatively low vapor pressures. I

Good results may be sion efiects on cathodes manufactured according to. the improved'process. There are also no changes of electron emissivity throughout the length of the coating caused by alkalmeearth metal condensin on the surface of the &

filament and flowing to the cold ends thereof. This may be the reason for the greater uniformity of the improved cathodes in respect to their electron emission properties. Particularly desirable results are obtained by heating the cathode to'such a temperature when the alkaline-earth meta-l vapor is being evolved, that the oxygen compound is partially evaporated or decomposed. This method yields cathodes having extremely high electron emissivity.

What I claim as new and desire to secure for electric discharge devices, said process including the steps of applying an oxygenous compound to a cathode foundation member and heating the oxidized member in the vapor of an electronically active material to a temperature so high that the said material is precluded from forming on the foundation member in a solid or liquid state.

2. A process of manufacturing cathodes for electric discharge devices, said process including the steps of coating a foundation metal of the cathode with an-oxygen compound and heating the coated metal in the vapor of an alkaline earth metal to a temperature exceeding 900 C. whereby the said metal is precluded from forming on the foundation member in solid or liquid state.

3. A' process of manufacturing cathodes for electric discharge devices, said process including the steps of applying a dissociable oxygenous compound to the surface of a cathode foundation member and heating said member in the vapor of an alkaline earth metal to a temperature so high that the said compound becomes partially decomposed and the alkaline earth material combines with the oxygen on the oxidized surface.

4. A process of manufacturing cathodes for electric discharge devices, said process including the steps of coating a foundation metal With tantalum oxide and heating the coated member in the presence of an alkaline earth vapor to a temperature of the order of 900 C.

In Witness whereof, I have hereunto set my hand.

ERICH WIEGAND. 

